Ultrasound systems exist today that utilize a variety of techniques for processing ultrasound signals to generate information of interest. For example, a variety of techniques exist today for performing beamforming upon ultrasound receive signals. One approach to beamforming performs Rf-beamforming upon analog or digitalized receive signals. Another approach to beamforming performs baseband beamforming upon digitalized receive signals. In the technical field of diagnostic, ultrasound imaging it is common practice to perform receive focusing in a dynamic way during the reception of the ultrasound signals, this realizes a certain sharpness over a wider depth range. However, in a dynamic receive focusing delay and sum beamforming technique, the signal delays are dynamically changing during the reception, as a result internal signal distortions become generated by the way of signal processing of the beamforming itself.
It is known in the technical field of diagnostic, ultrasound imaging, that the coherent summation process in the beamforming needs accurate fine-delay, realizing, low sidelobe-levels and good focus selectivity, and therefore high dynamic range. Several techniques are proposed for the fine delay, as interpolation and/or phase rotation. However, as phase rotations are computationally more effective, the phase rotation is not a true fine delay of the total-signal, but only a delay of the carrier part of the signal, the envelope of the signal is not fine delayed, this also results in the generation of signal-distortions in the beamforming. Correct fine delay of signals can only be performed by means of interpolation. However, it needs a high performance means of interpolation quality, to prevent signal-distortions produced by the interpolation. High performance interpolation in the beamforming requires a considerable computational burden. Poly phase interpolation is computationally more effective, but needs, in this case of ultrasound beamforming, a fine-delay control in each receive signal path, as a result, the signal processing of all the beamforming elements together becomes, at the end, very computationally intensive. Another solution is to use straight forward up-sample interpolation, which is computationally more intensive, but it can be split. The up-sampling part can be realized during the fine delay control in each receive signal path of the beamforming, and the computationally intensive filter-part of the interpolation, can be placed after the coherent summing of the beamforming. As a result it becomes a very computationally effective beamforming solution. However, also here, internal signal distortions become generated by the changing fine delay at the up-sample control stages, of this type of dynamic receive focusing beamforming.
Also common practice is the processing of multiple dynamic receiving focusing ultrasound beams, related to one ultrasound transmit event, this technique provides faster image frame-rates, but at the expense of lateral artifacts or loss of lateral sharpness. Synthetic Aperture and Retrospective Transmit Focusing in the technical field of diagnostic ultrasound imaging, provides some means to restore this kind of problems. As a consequence of these techniques, the ultrasound beamforming needs to provide a higher number of multiple dynamic receiving focusing ultrasound beams, with additional control of dynamic signal delays and apodizations. To realize a dynamic receive focusing multi-beam beamforming with a high performance fine-delay interpolation quality it becomes very computationally intensive.
Depth depending tracking filters, in here named as VCF, are also common practice in the technical field of diagnostic ultrasound imaging. During the reception of the ultrasound signals during the increasing time, relating to the reception of signals from the object of increasing depth, the signals become attenuated related to depth, and ultrasound frequency. The higher frequencies become more attenuated over depth then the lower frequencies, the effect is that at deeper locations the higher frequencies are severely attenuated, the high frequencies become hidden in the noise. To improve the SNR, depth depending tracking filters (VCF) are utilized, whereof, in traditional ultrasound systems the VCF is positioned after the beamforming. The presence of any kind of depth depending tracking filters after the traditional beamforming, will also result in internal signal distortion as a result of the traditional manner of delay and sum beamforming.
Further in the technical field of diagnostic ultrasound imaging, several other advanced techniques are utilized, like coded-transmission, or pulse-compression techniques, and several means of frequency-domain beamforming techniques are known.                With the coded-transmission, or pulse compression, the means of detection associated with these types of transmission, typically utilize some means of correlation techniques. The length, in time, of the used correlation template can be very long, resulting in filters with a large number of filter-taps.        The frequency-domain beamforming is mostly realized by some means of 2d spectral estimation, in combination with some means of interpolation in the 2d-frequency domain. The frequency-domain beamforming of other than linear array, is still very complex.        
It is the scope of the present disclosure to resolve several mentioned issues above, and to provide systems and methods for a distortion free ultrasound multi-line dynamic focusing beamforming.
A further object of the present disclosure is to provide for a method and an ultrasound system allowing a distortion free ultrasound multi-line dynamic focusing beamforming having further Retrospective Transmit focus capability, in a computationally effective manner.
Another object is to provide for a method and an ultrasound system allowing a distortion free ultrasound multi-line dynamic focusing beamforming allowing fine delay interpolation with reduce computational burden.